In electrostatographic printing, an electrostatic latent image is formed on a charge retentive surface. One type of electrostatographic printing is known as ionography. In ionography, a charge-retentive surface is charged in an imagewise fashion by the direct application of ions onto the charge retentive surface, known as a charge receptor. This latent image is developed by causing toner particles to adhere to the charged areas on the surface. The toner forming this developed image on the surface is then transferred to a sheet, such as of paper, and then the toner is fused on the sheet to form a permanent image.
U.S. Pat. No. 5,257,045 describes a particular kind of ionography which utilizes a "focused ion stream." In this type of ionography, a continuous stream of ions are emitted from an ion source, such as a corona wire, and are made available to a charge receptor on which a latent image is to be created. Disposed between the ion source and the charge receptor is an ion deposition control device, which is preferably in the form of a substrate interposed between the ion source and the charge receptor. The control device includes a plurality of apertures therein, through which ions can be selectively admitted from the ion source to selected positions on the charge receptor. Each of the apertures in the row has associated therewith a "pinch electrode" and one or more "displacing" electrodes. The purpose of the pinch electrode is to isolate a stream of ions from the radiations of ions which are generally being broadcast from the ion source and, in effect, to "funnel" the ion stream down to a much smaller predetermined cross-sectional width. By focusing the ion stream to a predetermined width, the ion stream can be directed to a suitably small spot size on the charge receptor, which in turn enables the creation of high-resolution latent images on the charge receptor. Displacing electrodes are used to direct this narrow beam of ions to the desired location on the charge receptor, so that a desired small area on the charge receptor may be charged according to its location in a desired image to be printed. The practical advantage of ionography with an ion stream is that the apertures can be made relatively large compared to the possible spot size of charged areas on the charge receptor, and therefore the ion deposition control device can be made quite cheaply.
The present invention exploits the principle of a "focused ion stream" known in electrophotographic printing and applies it to an electronic display.